Your request really seems to be for a bunch of people to draw a picture of a helmet, and whichever you think is the coolest one "wins." The problem with this approach is that farming your brainstorming and work out to amateurs/hobbyists/hopefuls and only actually paying the one you use is not business. That's not how it's done. If you honestly hired all these people, you'd need to pay them for the work they put in whether you decided to go with it or not.

What you seem to be doing (I think without realizing it) is holding a design contest. Why not just run with that? Plenty of real-world companies hold logo design contests or the like; people know what they're getting into when they enter a contest, no one expects it to be a job. Instead of your current approach, why not actually have a contest? You mentioned a Youtube channel that the winner would get promoted on, and payment for the person whose design you use. If you have a built-in fanbase, why not use it? The chance to have one's skills promoted to a wider audience and a one-time payment is a pretty crap salary, but it's not a bad first prize.